Which of the following describes a type of antenna loading?

When an antenna is physically too short for its operating frequency, it exhibits capacitive reactance, which prevents it from resonating efficiently. To counteract this, inductors (coils) can be inserted into the radiating elements to add inductive reactance. This technique is known as "loading." By adding these inductors, the antenna is "electrically lengthened," allowing it to resonate at a lower frequency without needing to be physically longer. This is very common in mobile HF antennas where a full-size antenna would be impossibly tall for a vehicle. The other choices describe mechanical changes rather than electrical ones. Installing a spring adds physical flexibility, strengthening elements resists wind, and inserting a resistor would only dissipate your transmitter's power as wasted heat instead of radiating it.